Reinforcements and Fillers

Fragrance enhancers, as their name indicates, are used either to eliminate undesirable odors or to produce desirable ones. Trash bags and kitty fitter liners, for example, may contain additives that absorb undesirable odors generated by their contents. Blow-molded bottles may also contain additives that prevent the product from picking up undesired odors from the surroundings, or that provide for generation of desired odors. Since odors and flavors are highly associated, these same additives can affect taste as well as smell. 

In some applications, it is useful to incorporate nonplastic substances into a plastic object, to reduce its cost or improve its performance in some way. Fillers are typically used to lower the cost of the plastic, and generally consist of minerals of some kind. Reinforcements are often more expensive, per unit mass or volume, than the plastics, but provide improvement in properties such as strength and/or rigidity. They usually consist of either organic or inorganic fibers. Use of fillers and reinforcements is less common in packaging applications than in uses such as automotive components or housewares, but is sometimes significant. In addition, these additives are more commonly used with thermoset polymers than with thermoplastics. 

The beneficial effects of surface treatments of filler particles, including silane treatments, are generally attributed to improved adhesion of the polymer to the filler surface. However, it should be realised that in many cases the changes in the degree of agglomeration brought about by the surface treatments are equally, or more, important [83]. 

Temperatures do not depend on the amount or size of filler. The values of the bulk moduli and the thermal expansion coefficients are independent of filler size, but depend considerably on the volume fraction of filler. All filled and unfilled materials show a glass-rubber transition, at which temperature the thermal expansion coefficient increases considerably and the bulk modulus decreases sharply [84]. The mineral fillers seem to modify mechanical properties on three levels [85, 86] in terms of their nature, their size, shape and distribution, and in terms of the changes they bring about in the microstructure of the matrix. 

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Polymers with differing morphologies respond differentiy to fillers (qv) and reinforcements. In crystalline resins, heat distortion temperature (HDT) increases as the aspect ratio and amount of filler and reinforcement are increased. In fact, glass reinforcement can result in the HDT approaching the melting point. Amorphous polymers are much less affected. Addition of fillers, however, intermpts amorphous polymer molecules physical interactions, and certain properties, such as impact strength, are reduced. 

Particulate fillers are divided into two types, inert fillers and reinforcing fillers. The term inert filler is something of a misnomer as many properties may be affected by incorporation of such a filler. For example, in a plasticised PVC compound the addition of an inert filler will reduce die swell on extrusion, increase modulus and hardness, may provide a white base for colouring, improve electrical insulation properties and reduce tackiness. Inert fillers will also usually substantially reduce the cost of the compound. Amongst the fillers used are calcium carbonates, china clay, talc, and barium sulphate. For normal uses such fillers should be quite insoluble in any liquids with which the polymer compound is liable to come into contact. 

There are a few excellent books dealing with the characteristics and properties of fillers. Two of the most interesting are Handbook of Fillers and Reinforcements for Plastics [37] and Handbook of Fillers [38]. 

MilewskyV (1978) In Handbook of fillers and reinforcements for plastics, Van Nostrand Rheinhold, New York, Ch. 3... 

In addition to the broad categories of TPs and TSs, TPs can be further classified in terms of their structure, as either crystalline, amorphous, or liquid crystalline. Other classes (terms) include elastomers, copolymers, compounds, commodity resins, engineering plastics, or neat plastics. Additives, fillers, and reinforcements are other classifications that relate directly to plastics properties and performance. 

For applications having only moderate thermal requirements, thermal decomposition may not be an important consideration. However, if the product requires dimensional stability at high temperatures, it is possible that its service temperature or processing temperature may approach its temperature of decomposition (Tj) (Table 7-12). A plastic s decomposition temperature is largely determined by the elements and their bonding within the molecular structures as well as the characteristics of additives, fillers, and reinforcements that may be in them. 

Note Adding certain fillers and reinforcements can raise decomposition temperatures. 

Composites (fibers, fillers, and reinforcements, design, tooling and manufacturing)... 

Intended to improve physical properties, reinforcements enhance the dimensional stability of materials, increase impact resistance, and improve tensile strength. The distinction between fillers and reinforcements is sometimes vague. Classification according to use. 

Fillers and reinforcements, in Plastics Compounding Redbook, Leonard, L. (Ed.), Advanstar Communications, Cleveland, OH, 2000, pp. 47-58. 

General chemical properties are subject to the compatibility of the fillers and reinforcements with the ambient conditions. If the fillers are well adapted, the chemical properties are the same for filled and neat polymers. 

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